An engine of a vehicle may include cylinder deactivation to improve engine efficiency. Engine cylinders may be selectively activated and deactivated to reduce engine pumping losses and adjust engine torque output. The engine cylinders may be activated and deactivated based on an engine torque threshold. For example, if the desired engine torque is greater than a threshold torque, all engine cylinders may be activated. If desired engine torque is less than the threshold torque, a fraction of engine cylinders maybe activated. Thus, the threshold engine torque is a condition for selecting between differing active cylinder displacements. However, it may not be desirable for the engine to switch between different active cylinder displacements at the same engine torque threshold at all times.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: varying an engine torque at which engine cylinders are activated in response to a compression ratio of the engine.
By adjusting an engine torque at which deactivated engine cylinders are reactivated in response to a compression ratio of an engine, it may be possible to provide the technical result of reducing the possibility of engine knock during cylinder reactivation. Further, it may be possible to increase engine efficiency since the method described herein provides a way to select different engine compression ratios in response to when the engine may operate more efficiently with the selected compression ratio.
In some examples, the torque threshold at which deactivated engine cylinders are reactivated may be adjusted in response to a rate of engine torque increase. For example, if engine torque is increased at a higher rate, the torque threshold at which deactivated engine cylinders are reactivated may be decreased as compared to the torque threshold at which deactivated engine cylinders are reactivated when engine torque is increased at a lesser rate. Further, adjustment of a compression ratio of the engine may be delayed until deactivated cylinders are reactivated when the rate of change in engine torque is greater than a threshold rate of change in engine torque.
The present description may provide several advantages. Specifically, the approach may reduce engine knock. Additionally, the approach may improve engine efficiency. Further, the approach may improve vehicle drivability by reducing the possibility of adjusting engine compression ratio at the same time cylinders are being activated or deactivated.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.